Some of the nominal screw sizes of self-tapping screws are 00, 0, 2, 4 and 6. A screw of size 00 with a round head has six thread starts and a maximum head diameter of 0.099 inches. Size 6 flat head screws have a maximum head diameter of 0.279 inches.
A self-tapping screw creates the hole it fits into on its own during drilling. The screws are available in different shapes and in different head types. Self-tapping screws are useful for joining two different materials together and when working with plastics, woods and metals. These screws are also used in objects that require frequent maintenance.